This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-377865, filed Dec. 12, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for ejecting liquid droplets, particularly, to a share mode type ink jet head.
2. Description of the Related Art
An apparatus for ejecting liquid droplets, e.g., a share mode type apparatus for ejecting liquid droplets, is widely known to the art. The apparatus is widely used as an ink jet head for ejecting an ink droplet.
An example of a conventional share mode type ink jet head (prior art 1) will now be described with reference to FIGS. 1 and 2. FIG. 1 is an exploded perspective view schematically showing an ink jet head as an apparatus of prior art 1. FIG. 2 is a vertical cross sectional view schematically showing the ink jet head shown in FIG. 1.
As shown in the drawings, the ink jet head of prior art 1 includes a rectangular piezoelectric body 10, which is thin and flat. A plurality of parallel grooves 12, which are arranged a predetermined distance P apart from each other in a predetermined arranging direction, are formed on a flat plane 10a of the piezoelectric body 10. These grooves 12 are equal to each other in size. Each of grooves 12 has a pair of ends. One end 12a of each groove 12 is open at one end surface 10b perpendicular to the plane 10a so as to form a nozzle-side opening. Also, the other end 12b of each groove 12 is formed such that the depth of the groove 12 is gradually decreased from the midway of the groove 12. As a result, the other end 12b does not extend to reach the other end surface 10c perpendicular to the plane 10a. 
Electrodes, which are not shown in the drawings for simplicity of the drawings, are formed on inner surfaces, i.e., a side wall and a bottom surface, of each of the plural grooves 12. A conductive pattern 14 is a conductive means formed together with the electrode and electrically connected to the electrode. The conductive pattern 14 is formed to extend in a region between the other end 12b of the groove 12 and the other end surface 10c on the plane 10a. 
A terminal flange 16a of a liquid supply section 16 is fixed to cover the entire open portion of the plane 10a in the region where the plural grooves 12 are open on the plane 10a. The terminal flange 16a has an ink outlet port 16c. The ink outlet port 16c communicates with a region in the vicinity of the other end of the opening of each groove 12 on the plane 10a. The liquid supply section 16 also includes a small ink container 16e equipped with a connection plug 16d. A flexible ink supply pipe (not shown) extending from an ink supply source such as an ink tank (not shown) is connected to the connection plug 16d. The small ink container 16e includes an ink reservoir 16f into which the ink from the ink supply pipe flows through the connection plug 16d. The ink reservoir 16f is fixed to cover the ink outlet port 16c on the surface opposite the surface facing the plane 10a of the piezoelectric body 10 in the terminal flange 16a. An ink filter 16g is arranged within the ink reservoir 16f. 
One end portion of a flexible substrate 18 is fixed to the region to which the plural conductive patterns 14 extend on the plane 10a. A plurality of conductive patterns 18a is formed on the flexible substrate 18. The conductive patterns 18a is electrically connected respectively to the conductive patterns 14 of the piezoelectric body 10. Also, a driving circuit 18b is fixed to the flexible substrate 18. The driving circuit 18b selectively transmits the voltage supplied from an outer power source (not shown) to the conductive pattern 14 as a driving signal.
A nozzle plate 20 covering the end 12a of each of the grooves 12 is fixed to the end surface 10b of the piezoelectric body 10. A plurality of nozzles 20a is formed in the nozzle plate 20. Each of the nozzles 20a is arranged substantially in the center of one end 12a of each groove 12. An ink repelling treatment is applied to the outer surface of the nozzle plate 20 on the side opposite the surface facing the end surface 10b of the piezoelectric body 10.
First, The ink jet head of prior art 1 pressurizes the ink in the ink supply source, and supplies the ink to the ink reservoir 16f through the ink supply pipe and the connection plug 16d. The ink thus supplied into the ink reservoir 16f flows into all the grooves 12 of the piezoelectric body 10 through the ink filter 16g and the ink outlet port 16c. It is possible for the ink filling the plural grooves 12 to leak to the outside through the plural nozzles 20a of the nozzle plate 20. However, the ink is repelled by the outer surface of the nozzle plate 20 and, thus, is not attached to the outer surface of the nozzle plate 20.
A pressure of the ink within the groove 12 is reduced to negative pressure relative to the atmospheric pressure when the pressurization is released. As a result, the ink forms a meniscus because of the surface tension within each nozzle 20a. 
While the ink is held under this state, the driving circuit 18b selectively impresses a driving signal (driving voltage) to the electrode within the groove 12 in accordance with the control signal generated from a control circuit (not shown), e.g., a control circuit of a personal computer connected to the ink jet printer using a conventional ink jet head. As a result, the side wall of the groove 12 corresponding to the electrode to which the driving signal is impressed is deformed so as to reduce the lateral cross section. When area of the lateral cross section is reduced in the groove 12, the ink in each groove 12 receives a shock wave. A predetermined amount of the ink is ejected outward from the corresponding nozzle 20a in the form of ink droplets.
The grooves 12 are formed by applying a rotary cutter blade to the plane 10a of the piezoelectric body 10. In each of the grooves 12, the side wall between the adjacent grooves 12 are formed deformable and have sufficient durability. Such being the situation, it is necessary for the side wall between the adjacent grooves 12 to have a reasonable thickness. Because of the particular requirement, the highest groove density achieved nowadays is about 200 grooves/inch (25.4 mm). In general, 180 grooves are formed per inch. In other words, the nozzle density (density of the ejected ink droplets) of the ink jet head using a piezoelectric body thus manufactured is 180 dpi.
The construction of a share mode type ink jet heat of prior art 2 will now be described with reference to FIGS. 3 and 4. FIG. 3 is an exploded perspective view schematically showing the ink jet head of prior art 2, and FIG. 4 is a vertical cross sectional view schematically showing the ink jet head shown in FIG. 3.
The ink jet head of prior art 2 is constructed such that the density of the ejected ink droplets is set at 360 dpi, which is twice the density for the ink jet head of prior art 1.
As shown in FIGS. 3 and 4, the ink jet head of prior art 2 includes two ink jet heads of prior art 1. The two ink jet head is joined to each other such that other surfaces (on the back side of the plane 10a) of the piezoelectric bodies 10 stand opposite to each other. It should be noted that, in the ink jet head of prior art 2, the piezoelectric bodies 10 are joined to each other such that a plurality of nozzles side openings (i.e., opening of one end 12a of each of the grooves 12) on one end 10b of one of the piezoelectric bodies 10 are deviated by half the pitch P, i.e., xc2xdP, from the nozzles side openings of the other piezoelectric body 10 in the arranging direction of the nozzle-side openings, as apparent from FIG. 3.
Also, in the ink jet head of prior art 2, the end surfaces 10b of the two piezoelectric bodies 10 are arranged on the same plane, and a common nozzle plate 20xe2x80x2 is fixed to the end surfaces 10b of the two piezoelectric bodies 10. A plurality of nozzles 20xe2x80x2a are made in the nozzle plate 20xe2x80x2. Each of the nozzle 20xe2x80x2a is substantially aligned with the center of each nozzle-side opening of the two piezoelectric bodies 10.
As described above, the common nozzle plate 20xe2x80x2 is used in the ink jet head of prior art 2. Therefore, if The nozzle-side openings of the two piezoelectric bodies 10 deviate to the predetermined position, the position relations of each nozzles 20xe2x80x2a can be set up in each other precisely.
In the ink jet head of prior art 2, a pair of flexible substrates 18 are fixed to a region on the side of the other end surface 10c in the plane 10a. The planes 10a of the two piezoelectric bodies 10 face in the opposite directions to each other. Also, the driving circuits 18b are fixed to the flexible substrates 18 such that these driving circuits 18b are positioned to face each other. In other words, the driving circuits 18b are covered with the flexible substrates 18 so as to be protected from external impact.
However, in the ink jet head of prior art 2, the terminal flange 16a and the small ink container 16e of the liquid supply section 16 are fixed in a manner to protrude greatly in the opposition direction (in the vertical direction in FIG. 4) from each of the plane 10a of the two piezoelectric bodies 10.
In recent years, required is an ink jet printer capable of recording an image smaller in the granular feel at a high speed and with a high resolution. In order to suppress the granular feel, it is necessary to decrease the size of each ink droplet. Where the size of the ink droplet is reduced, it is necessary to increase the nozzle density of the ink jet printer so as to fill a predetermined printing area with ink droplets at a high speed.
In order to increase the nozzle density, it is effective to use two ink jet heads in combination as in the ink jet head of prior art 2. Where the nozzle density is to be further increased in the conventional ink jet printer, it is conceivable to increase the number of ink jet heads of prior art 2. In this case, the weight of the carriage having the ink jet head mounted thereon is increased in such an ink jet printer. Therefore, it is difficult to scan the ink jet head at a high speed. Also, in the ink jet head of prior art 2, it is necessary to align one ink jet head with the other ink jet head accurately in the assembling operation such that the nozzles are aligned with a predetermined accuracy. It follows that the assembling operation is rendered troublesome in the ink jet head of prior art 2.
Also, even if the nozzle density is to be increased by combining a plurality of piezoelectric bodies 10 as in the ink jet head of prior art 2, a difficulty remains unsolved in respect of the arrangement of the liquid supply section 16 and the flexible substrate 18 used as a means for transmitting electric signals. In view of the arrangement of the liquid supply section 16, etc., it is possible to combine at most two piezoelectric bodies, resulting in failure to increase sufficiently the nozzle density of the ink jet head.
An object of the present invention, which has been achieved in view of the situation described above, is to provide An apparatus for ejecting liquid droplets such as an ink jet head, which permits increasing easily the density of the nozzles and also permits the manufacture with a low cost.
Another object of the present invention is to provide an apparatus for ejecting liquid droplets such as an ink jet head, which permits increasing easily the image density and also permits the manufacture with a low cost.
According to an aspect of the present invention, which is intended to achieve the objects described above, there is provided an apparatus for ejecting liquid droplets, comprising:
a plurality of plate-like piezoelectric bodies, each of the piezoelectric bodies including a pair of a primary surfaces, a pair of end surfaces, and electrodes, one primary surface on which a plurality of grooves are formed, the grooves arranged in parallel a predetermined distance apart from each other, each of the grooves having a pair of ends, the one end surface differing from the primary surface, one end of each of the parallel grooves being open in the one end surface, a plurality of nozzles being arranged to conform with the plural openings, the electrode formed on a inner surface of each of the grooves, the primary surfaces of the plural piezoelectric bodies facing the same direction, and the adjacent piezoelectric bodies stacked on the primary surfaces; and
a liquid supply path that supplies a liquid to the plural grooves, the liquid supply path being common to the plural piezoelectric bodies;
such that the grooves is supplied with liquid, and a cross section of the grooves is changed to eject the liquid through the nozzles when a voltage is impressed to the electrodes.
As described above, plate-like piezoelectric bodies each having a plurality of parallel grooves formed therein are stacked one upon the other in the present invention. It is theoretically possible to stack an innumerable number of piezoelectric bodies, which are lightweight and compact. Therefore, the apparatus may be provided with a large number of nozzles arranged at a very high density. In addition, a liquid supply path that supplies a liquid to the plural grooves, the liquid supply path being common to the plural piezoelectric bodies. The liquid supply path may supply a sufficiently large amount of a liquid to the plural grooves of the stacked plural piezoelectric bodies through itself. It follows that the construction of the liquid supply sections remains to be simple even if the number of piezoelectric bodies stacked one upon the other is increased.
Various embodiments of the present invention and modifications thereof will now be described with reference to the accompanying drawings.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.